Tectonic ImpactsGlossary

Term Meaningaerosol A small droplet of liquid is suspended in airandesite A fine-grained igneous volcanic rock crystalized from magmas from at

subduction zones.anticline Folds where the limbs either side of the fold axis are bent downwardsaphanitic A rock texture in which crystals are too small to be identified without a

microscope.assimilation The process in which a rock melts and becomes part of a magmaasthenosphere

A region made up of partially molten rock bellow the lithosphere

basalt A dark, fine-grained volcanic rock that sometimes displays a columnar structure

Benioff zone An inclined area of earthquake activity dipping into the mantle away from a trench

conservative boundary

In relation to plates, it describes a boundary where crust is neither created of subducted

constructive boundary

In relation to plates, it describes a boundary where new ocean crust is formed

continental drift

The gradual movement of the continents across the earth's surface through geological time.

convection The process in which heat is transferred by the motion of material in a fluid

convergent boundary

when two crustal plates move towards each other and collide

destructive boundary

In relation to plates, it describes a boundary where crust is being subducted into the mantle

divergent boundary

Where two plates diverge or separate from each other

earthquake A sudden and violent shaking of the ground, sometimes causing great destruction, as a result of movements within the earth's crust

fault A fracture in a rock where there has been relative movement on either side of the fracture

felsic High in silica, low in iron, light in colour, less dense, found in continental crust, associated with volcanoes

focus The point beneath the Earth’s surface where rocks break and shock waves are produced generating earthquakes

Fold mountain A mountain containing rocks deformed by horizontal forces and intruded by igneous rocks

geosyncline The thick accumulation of sediments formed near mountain belts.Gondwana A vast continental area believed to have existed in the southern

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hemisphere and to have resulted from the breakup of Pangaea in Mesozoic times. It comprised the present Arabia, Africa, South America, Antarctica, Australia, and the peninsula of India

granite A very hard, granular, crystalline, igneous rock consisting mainly of quartz, mica, and feldspar

granulites Rocks formed under high temperature and pressure. Water-containing minerals, such as mica nad amphibole, are absent.

greenhouse gases

Gases that increase the heat retained in the atmosphere

intra-plate Within a plateisostatic adjustment

Movement that balances weight forces and buoyancy forces

lahar Mud flowsLithosphere Consists of a series of plates, called lithospheric plates, which ride and

move on the partially molten asthenosphere. The lithospheric plates move relative to each other. They are created at mid-oceanic ridges and destroyed at subduction zones.

Laurasia A vast continental area believed to have existed in the northern hemisphere and to have resulted from the breakup of Pangaea in Mesozoic times. It comprised the present North America, Greenland, Europe, and most of Asia north of the Himalayas

Ma An abbreviation meaning ‘million years’. “M” represents ‘mega’ or ‘million’, and “a” represents annum or year.

mountain A large natural elevation of the earth's surface rising abruptly from the surrounding level; a large steep hill

mid-ocean ridge

A giant mountain range that lies under the ocean and extends around the world where sea floor spreading occurs

mafic High in iron, slightly denser, darker in colour, low in silica, found in oceanic crust

ophiolite Rocks found on land that have an origin as oceanic crustorogeny Episode of mountain buildingPangaea A supercontinent comprising all the continental crust of the earth,

postulated to have existed in late Paleozoic and Mesozoic times before it broke into Gondwana and Laurasia

peridotite Dark coloured, coarse grained ultramafic rock containing olivine and pyroxene

pillow basalt Basalt with a pillow-like structure due to be erupted in waterplate Any of several large pieces of the Earth's lithosphere which participate in

plate tectonicsplate tectonics The lithosphere is being recycled down trenches at subduction zones. As

new sea floor is being produced at the mid oceanic ridge, old sea floor is being removed at the trenches

platforms Areas with relatively flat surfaces formed on continentsplutons Masses of igneous rocks formed below the earth’s surface.porphyritic A rock texture in which some crystals are significantly larger than othersP-wave Type of earthquake wave that can travel through solids and liquids

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pyroclastic Fragmented rock material formed in a volcanic eruptionreverse faults Steep faults caused by compressional forcesrhyolite A fine grained volcanic igneous rock with the same composition as granite.sea floor spreading

The formation of new areas of oceanic crust, which occurs through the upwelling of magma at mid-ocean ridges and its subsequent outward movement on either side

seismometer An instrument that records earthquake or other seismic wavesshield Old parts of continents composed of rocks formed deep in the Earthsilica Silicon dioxidesubduction The sliding of the sea floor beneath a continent or island arc. Lithosphere

is consumedsyncline Folds where limbs either side of the fold axis are bent upwardstransform boundary

A fault which runs along the boundary of a tectonic plate

troposhere Layer of the atmosphere in which clouds formtsunami A water wave with a very long wavelengthultramafic An igneous rock composed only of minerals rich in iron and magnesiumviscous The property of a fluid that describes it resistance to flow. A very viscous

fluid does not flow easily.Volcanic island arc

An arc of volcanic activity marked by a chain of volcanic islands. It lies parallel to an ocean trench.

analyse Identify components and the relationships among them, draw out and relate implications

assess Make a judgment about the value of somethingcompare Show how things are similar or differentdeduce Draw conclusionsdefine State the meaning of and identify essential qualitiesdiscuss Identify issues and provide point for and againstdistinguish Recognize or note/indicate as being distinct or different from, note

differences between thingsevaluate Make a judgment based on criteriaexamine Inquire intopredict Say what might happen based on available datasummarize Express concisely the relevant details

Focus Area 1-Lithospheric plates and their motion

-Describe the characteristics of lithospheric plates:

Upper layer of each lithospheric plate is composed of crust Crust is composed of either continental crust or oceanic crust Continental crust is typically made up of relatively less dense rock like granite Oceanic crust is typically made up of more dense rock like basalt Oceanic crust carries sediments that have been deposited on the oceanic floor Some lithospheric plates have just oceanic crust Others have some oceanic crust and some continental crust

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Oceanic crust is general thin, usually between 5 and 10km thick Continental crust is generally between 25 and 50 km thick Under large mountain ranges the crust can be over 80 km thick The lithospheric plates are up to 70km thick, where there is oceanic crust, and up to

150km thick, where there is continental crust Under large mountain ranges the crust can be over 80 kilometres thick

Feature Continental OceanicAverage Density 2.7g/cm³ 3.0g/cm³Average Thickness 35km 7kmComposition Felsic rocks, sedimentary, igneous,

andesite and graniteMafic rocks, basalt and gabbro

Oceanic crust Similarities and differences

Continental crust

Thinner ThickerMore Dense Less denseMafic FelsicHigh in iron Both contain iron Low in ironLow in silica Both contain silica High in silicaDarker in colour Higher in colourCreates sedimentary rocks Creates igneous and metamorphic rocks-Identify the relationship between the general composition of igneous rocks and plate boundary type:

At divergent boundaries the dominant types of igneous rocks are the mafic igneous rocks like basalt, gabbro and peridotites

Mafic rocks are dark coloured because they contain minerals richer in magnesium and iron like olivine, pyroxene and amphibole and biotite

Mafic rocks at divergent boundaries form as a direct upwelling of dense magmas from the asthenosphere

At convergent boundaries the dominant types of igneous rocks are felsic rocks like andesite, rhyolite and granite

Felsic rocks are light coloured because they contain more feldspar and quartz Minerals with relatively more silica than the dark coloured minerals Felsic rocks are produced from magmas with higher water content Occasionally at conservative boundaries a variety of igneous rocks occur as molten

rock fills cracks to form intrusions, such as dykes and sills Compare samples of andesite, basalt, granite, gabbro, diorite and rhyolite:

1. Create a table to tabulate their physical characteristics, mineral composition and typical boundary location to illustrate trends

Granite Diorite Gabbro Rhyolite Basalt AndesiteCharacteristics Pale

colour, specks of pink black

White grey and black specks, mostly dark

Dark grey with black specks, small

Grey with red streaks, small

Fine crystals, dark grey

Grey, small white speckles

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and grey, large crystals

in colour, large crystals

crystals crystals

Volume 4 cm3 4 cm3 7 cm3 6 cm³ 3 cm³ 17 cm³

Mass 10.7 g 9.4 g 18.8 g 14 g 7 g 43.1 gDensity=mass/volume

2.67 2.35 2.7 2.3 2.9 2.5

2. Write a procedure for measuring the density of an irregular shaped object.Title: Measuring densities of irregular shaped objects.Aim: To measure the densities of an object with an irregular shape.Hypothesis: We will find out the density by finding out the mass and the volume of the object.Equipment and risk assessment:

Equipment Potential Hazard Prevention or controlWater Spilling the water on the

floor then slipping on itHandle water carefully and wipe up all spills immediately

Measuring cylinder

Dropping it and it smashes

Keep measuring cylinder in the centre of the table at all times and clean up immediately if you do drop it. Handle with caution

String Getting a rope burn Do not let the string slide on your skin rapidly, hold with a tight grip at all times

Various different shaped rocks

Getting a cut from a sharp edge on the rock

Be gentle with all rocks and avoid rocks with sharp edges

Measuring scales Dropping them and they land on someone's feet

Keep on the table at all times, do not remove

Method: 1. Fill a measuring cylinder with 40mL of water2. Tie a knot using the string around one rock and make sure it is firmly tied3. Gently lower the rock using the string into the measuring cylinder until it reaches the bottom. Keep hold of the string.4. Measure the volume of water now. Be cautious of parallax error5. Subtract the original volume of water from the new volume, this will give you the volume of the rock6. Take the rock out of the water and untie the knot7. Measure the rocks mass using the measuring scales.8. Divide the mass by the volume to find out the density.9. Repeat steps 2 to 8 three times to make sure your result is accurate.10. Repeat these steps with all of the other rocks. Summary:Rocks with a higher density had a higher crystal content and contained more minerals

-Outline the motion of plates and distinguish between the three types of plate boundaries (convergent, divergent and conservative): Plates move slowly, at speeds of up to 12cm per year

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Plates are created at divergent boundaries, slide past each other at conservative boundaries and are absorbed back into the earth at convergent boundaries

At divergent zones, the plates are moving away from each other and new oceanic lithosphere is created to fill the gap

Divergent boundaries are usually found at the mid-ocean ridges Some special cases of divergent boundaries can be found in rift valleys on continental

crust where the continent is beginning to divide e.g. the Africa Rift Valley, the Dead Sea Rift Valley

At conservative plate boundaries, crust is neither created nor destroyed The plates slide past each other along faults. Near mid ocean ridges these faults are

called transform faults On continental crust, these boundaries are the cause of many earthquakes e.g. Alpine

Fault System in NZ and the San Andreas Fault in California, USA. At convergent zones, the lithosphere is consumed. This occurs when one plate, usually

consisting of oceanic material, is subducted beneath another plate. Deep ocean trenches usually found along a continent’s edge when subduction occurs Quite often, the upper surface of the subducted plate is shaved off, creating folded

sediments at the edge of the overlying plate. As the subducted plate moves deeper into the asthenosphere, it partly melts and this motel rock rises because it is less dense than the material above it

Motion Plate Type Major geological features Examples Divergence -Ocean –

Ocean divergent zone-Mid-ocean ridge-Ocean spreading zone

Volcanoes (non-explosive) e.g. shield volcanoes, fissure volcanoes, cinder conesMountainsNew ocean crust

Basalt rock from basaltic lava (low viscosity, low in silica, mostly dark, mafic minerals high in iron and magnesium)Pillow basaltNormal faultsShallow earthquakes

Mid-Atlantic Ridge (Eurasian and North American Plates)

Iceland

-Continent – Continent-Continental Rift Zone

Volcanoes (non-explosive) shield volcanoes, cinder conesMountainsRift valleysNew ocean crustBasalt rock cools from from basaltic lava (low viscosity, low in silica, low gas content, mostly dark, mafic minerals high in iron and magnesium)Normal faultsShallow earthquakes

Great East African Rift Valley (African, Arabian and Indian plates)

Convergence -Ocean-Ocean

-Subduction

More dense ocean plate subducts less dense continental plateReverse faultsVolcanoes form an island arcStrato-volcanoes

Japan Islands (Eurasian plate and Indo-Australian Plate)

Marinana Trench

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Explosive volcanism as lava is viscous being high in silica, high gas contentMostly felsic minerals which are light colouredLava cools to form andesite and rhyolite rocksStrong earthquakes (Benioff Zone)Ocean trench

(11 km)

-Continent –Continent

No subduction as both plates low densityMassive fold mountainsCrustal thickening and shorteningShallow to deep earthquakesVery little volcanismReverse faultsFoldingRegional metamorphism of rocks (gneiss, schist)Granite plutons from deep melting of crust beneath mountains

Himalayas (Indo-Australian Plate and Eurasian Plate)

-Ocean-Continent

-Subduction

Dense ocean plate subducts less dense continental plateSome fold mountains as crust pushed upReverse faultsStrato-volcanoesExplosive volcanism as lava is viscous being high in silica, high gas contentMostly felsic minerals which are light coloured

-Gather and analyse information from secondary sources about the forces driving plate motion:

The main forces behind plate motion are convection currents, gravity and heat With plate tectonics subducting through the crust how they begin to move is by motion

of convection currents beneath the earth's surface in the mantle The convection currents are stimulated and powered by heat and from this heat,

convection cells begin to rotate causing crust movement above in the lithosphere As the plates begin to subduct ridge pull and slab push are factors that contribute to the

gravitational pull that drives the plates down into the mantle

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With mid-ocean ridges spreading the sea floor and pushing away from the ridge the slab push and then as the crust descends ridge pull carries the plate

Convection currents in the asthenosphere contribute most to the movement of lithospheric plates

-Describe current hypotheses used to explain how convection currents and subduction drive plate motion: Idea 1: The plates move because of convection currents in the asthenosphere which

transfer heat from the lower mantle towards the crust. As the currents move they drag the plates with them (shear traction)

Idea 2: The higher density of cold rock compared to that of hot rock causes the lithosphere to be dragged by gravity (ridge-push) from the relatively high mid-ocean ridge to the subduction zone by the sinking denser lithosphere (slab-pull)

Idea 3: A tensional force is placed on an upper plate caused by subduction of the lower plate. The subducting zone moves away (called roll-back) from the upper plate to create secondary volcanic arcs (trench suction)

Convection Currents3 forces: convection currents, slab pull, ridge push

Materials: -Water (hot and cold)-Food colour x2 (red and blue)-Clear plastic tray (8" or greater), radial ridges not concentric ridges-Eyedropper-4 Styrofoam cupsProcedure:

1. Fill tray with cool water. Place tray on top of 3 evenly spaced, inverted Styrofoam cups. (This should well support your display) 2. Fill the 4th cup with hot water and slide under the centre of the tray. 3. Using the eyedropper, gently place a blob of food colour inside the tray, on the bottom directly over the heat source. 4. A second colour can be added to the outside edge of the tray, away from the heat source, (again on the bottom). 5. Observe 5 minutes

Discussion questions: Which way does the warmed water move? Towards the centre of the heat source What happens when it reaches the surface? It spreads away from the heat source and

then sinks again. Which way does the cooler water on the edges move? Down

Focus Area 2-Mountain building

-Distinguish between mountain belts formed at divergent and convergent plate boundaries in terms of general rock types and structures, including folding and faulting

Divergent boundariesMountain belts formed from the action of thermal uplift and rifting are of two main types:

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1. Mid-ocean ridges form a near-continuous underwater mountain chain that extends for 60 000 kilometres right around the globe. Mid-ocean ridges rise to over 2.4 kilometres above the floor of the 5 kilometres deep ocean basins. A mid-ocean ridge can be a wide a 2000 kilometres.Mid-ocean ridges result from convective upwelling of mantle beneath thin oceanic lithosphere. They are formed along structurally weak zones created where the ocean floor is being pulled apart lengthwise along the ridge crest. New magma from deep within the Earth rises easily through these weak zones and eventually erupts along the crest of the ridges to create new oceanic crust. This process is called seafloor spreading.At the top of the oceanic crust at mid-ocean ridges are basalt lavas. The lavas often form as pillow lavas. Beneath are numerous basaltic dykes and deeper down are gabbros. The topography near the ridge axis is very rough and mountainous. At the centre of each ridge there are steep-sided troughs, several kilometres wide, which are similar to rift valleys that occur on continents. Mid-ocean ridges are offset by transform faults that run perpendicular to the ridge axis. The faults are only active between the spreading centres.

2. Young rift zones occur within continental landmasses and are caused by convective upwelling of mantle beneath weak continental lithosphere. When continental crust stretches beyond its limits, tension cracks begin to appear on the Earth's surface. Magma rises and squeezes through the widening cracks, sometimes to erupt and form volcanoes. Rift zones generally have intensive basaltic igneous activity. The rising magma, whether or not it erupts, puts more pressure on the crust to produce additional fractures and, ultimately, the rift zone. The uplift produces plateaus adjacent to the rift. These plateaus generally slope upwards towards the rift valley. Escarpments in the rift valley are formed from normal faulting into the rift. Such features are seen in Africa along the East African Rift Zone.

Convergent boundariesThe three types of convergent boundaries result in the following mountain types:Ocean/ocean boundaries:Mountains formed at ocean/ocean boundaries are of the volcanic island arc type. They form

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on an oceanic plate that has another oceanic plate subducting under it. There are two types of mountains that can form at ocean/ocean boundaries.

1. Those that comprise elongated mounds of ocean floor sediments that have been tightly folded and chaotically mixed in the trench by the faulting and folding caused as they are scraped from the down-going oceanic plate. The southern line of islands of the Indonesian Archipelago is a good example of this type.

2. Those formed of chains of explosive volcanoes. These volcanoes form from andesitic magmas that are generated as the subducted plate partially melts when it comes in contact with the hot asthenosphere. Steam and other volatile substances find paths upwards, creating vents for magma to reach the surface to create the volcanoes. The northern line of islands of the Indonesian Archipelago is a good example of this type. Island arcs can be deformed by strike-slip faults and folds.

Ocean/continent boundaries:As an oceanic plate is subducted beneath a continent, the sediments on the upper surface of the lower plate will be scraped off to produce a wedge of sediment called an accretionary wedge. Where the accretionary wedge is forced directly against the leading edge of continental crust, the subducting plate will be forced down steeply into the asthenosphere where the plate will be partially melted. Steam produced in the process also partially melts the upper mantle. Andesitic magmas are produced from these processes. Mountains will be produced in the continental plate from the compression and uplift of the low density wedge sediments and the sediments and rocks of the continent, and from the intrusion of magma produced from the partial melting in the subduction zone. These mountains rise to very high altitudes and contain highly folded and faulted sedimentary rocks produced from the compressional forces. The upper sections of sedimentary mountain ranges remain poorly consolidated and quickly erode, producing large amounts of sediment for the rivers that drain from them. The intrusions of magma are in the form of large granitic batholiths beneath the volcanic belt. The mountains contain explosive andesitic volcanoes. The explosive volcanoes produce much pyroclastic sediment that is deposited in the mountain areas. The explosive volcanoes frequently form calderas where they develop from eruptions from large, shallow magma chambers. The Andes Mountain chain in South America is a good example of this ocean/continent type of mountain building.

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Continent/continent boundaries:

When two continents collide, the ocean between them has been subducted under one of them. The continents will have been flanked by accreted sediment from the ocean floor that was scraped off from the subduction. This sediment forms into a huge wedge as it is folded, compressed and uplifted. Rocks from old oceanic plate, called ophiolites, can also be squeezed between the two continents and be uplifted as part of the mountain range formed. Ophiolites are very mafic and are composed of rocks like basalt and gabbro. Eventually the two older sections of colliding continents meet. These older sections of the continents are called cratons. Cratons are made up of crystalline igneous and high-grade metamorphic rocks. They are old and incompressible. The rocks of the craton splinter and fault at low angles, stacking on each other as they are compressed to form mountains. The Himalayas are an example of a mountain range that has been formed from compressed ocean floor sediments and fractured cratons. Low-angle thrust faults are common.

-Gather, process and present information from secondary sources which compares

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formation, general rock type and structure of mountain belts formed as a result of thermal uplift and rifting with those resulting from different types of plate convergence

Mountain belts

Mountain belt features

formed by: Formation General rock type Structure of mountain belts

Ocean-ocean boundaries

Occurs when two plates converge-one edge of the ocean crust is subducted beneath the other at an ocean trench

Felsic minerals-Andesite and rhyolite

Island arcs and chain

Ocean-continent boundaries

Occurs when oceanic crust is subducted under continental crust which forms an active continental margin between the subduction zone and the edge of the continent

Felsic minerals-andesite and rhyolite

Intensely folded mountain ranges

Continent-continent boundaries

Results when two continents collide. The continents were serparated at one time by oceanic crust that was progressively subducted under one of the continents. No subduction as both plates have low density

Metamorphism of rocks: gneiss and schist

Intensely folded mountain ranges

Focus Area 3- Continents evolve as plate boundaries move and change

-Outline the main stages involved in the growth of the Australian continent over geological time as a result of plate tectonic processes

It is important to understand that the Australian landmass has existed as an island as we know it since about 55 million years ago (mya). Any outline of how the Australian continent has grown must be set in the broader context of a smaller Australia linked to other landmasses, particularly to the west and south. Often the eastern border met ocean with island arcs or with shallow seas.

The oldest rocks of Australia are found in Western Australia and are 3800 million years old. They are found in cratons, areas that have been through a full cycle of continental crust building processes. An area is cratonised when it has been through stages of mountain building that includes folding, igneous emplacement and crustal thickening, and has become stable after continuous erosion and isostatic uplift until it is about 35 kilometres thick.

The general trend across Australia is that the rocks become younger as we move from west to east.

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Stage 1: Formation of cornerstone blocks (cratons)-By 2500 mya, three large cratons were established in Western Australia.Stage 2: Welding the blocks together-From 2500mya to 900 mya, the cratons were separated by active, linear mountain chains, known as mobile belts, that welded the cornerstone blocks together. These belts were highly deformed and folded and contain metamorphic rocks and granite.-By 900 mya, the western two thirds of present day Australia had been cratonised. Australia was still part of Gondwana. Stage 3: Subduction and accretion in the east.-From about 500 mya to about 250 mya, the continent was developed further to the east in the formation of the Tasman Fold Belt. The rocks present in the eastern third of the Australian continent exhibit evidence of former island arcs and ocean trenches resulting from the subduction of an oceanic plate. Sediment accumulated between the continental edge and the island arc, filling the seaway.-From 320 mya to 280 mya, major mountain building occurred in eastern and central Australia, including the formation of the Lachlan Fold Belt and the New England Fold Belt. These belts supplied the sediment for sedimentary basins that developed along the eastern flank of Australia. The active, or mobile, belt then moved eastward to produce the Lowe Howe Rise. The current mobile belt lies along the Tonga-Kermadec-New Zealand Line in the Pacific Ocean.-By 200 mya, the eastern third of Australia was cratonised.Stage 4: Shallow seas-160 mya, an area called Argoland rifted away to the northwest. Rift valleys formed down the Western Australian coast and between Australia and the Indian continent. This was the beginning of the breaking up of Gondwana. sea levels rose, flooding over the Great Artesian Basin.-132 mya, a narrow seaway had developed separating Argoland. South and west of Australia, spreading began and marked out the continental shapes including India. Faster spreading between India, Antarctica and Australia continued to 118 mya, opening an ocean up to 600 kilometres wide.-96 mya, the Lord Howe rise began rifting south of Tasmania and westward, separating Antarctica. The rift that was moving India away was cut.-84 mya, the Indian continent moved further north with the same direction as the rift between Australia and Antarctica.-64 mya, the Tasman Sea continued spreading, until 49 mya when spreading stopped.-From 45 mya to the present, the Southern Ocean continued spreading. Resultant downwarping of the continent allowed shallow seas to cover the Murray Basin.Stage 5: Intra-continental earthquakes and hot spot volcanoes-As the continent (now the island we recognise) continued its northward drift, it passed over a number of mantle hot spots, resulting in a series of parallel lines of volcanoes which are younger towards the south. The largest of these include Mount Warning on the NSW/Queensland border and Mount Canobolas in the NSW Central West. The most recent volcanic eruption was at Mount Gambier in South Australia only 4000 years ago-Tensional stresses acting within the continent as the plate boundary to the north pushed against the Asian and Pacific plates caused some very old faults to move periodically, and blocks to adjust isostatically. The Great Dividing Range was uplifted to its present height by this process.

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Stage 6: Continuing northward-Interaction between the converging Australian and Pacific plates has produced the current New Guinea mobile belt.

-Summarise the plate tectonic super cycleThe plate tectonic super-cycle is a theory to explain a sequence of events that have repeated at least three times. Formation of super-continents Pangaea and Rodinia occurred 300 million years ago and 900 million years ago, suggesting a super-cycle time span for formation and breaking up of super-continents of about 600 million years.

The following is a very general description of possible super-cycles.

During plate tectonic development, a super-continent breaks up and the two new continents become separated by the new oceanic lithosphere that is produced at a mid ocean ridge between them. As the oceanic lithosphere grows, the continents drift further apart. If a subduction zone forms near the edge of one of the continents, the oceanic lithosphere will be consumed in the subduction zone. The continents will be drawn back together, eventually to collide producing a super-continent again.

If a subduction zone develops on the far side of one of the continents, oceanic lithosphere will be consumed. This may eventually cause the continent to collide with another continent producing a new super-continent.

The following is another super-cycle scenario, using Pangea as an example:

Begin with a small super-continent, like Pangea, completely surrounded with ocean. (Pangea occupied 30% of the Earth's surface with the other 70% being ocean.)

Spreading at a mid ocean ridge some distance from the super-continent will cause the oceanic lithosphere near the super-continent to begin to subduct beneath it.

This subduction produces the characteristic andesitic volcanoes. The volcanism at the edges of the super-continent causes some weakness in the crust there.

Subduction continues until the subduction zone becomes choked and ceases, causing a new subduction zone to develop a few hundred kilometres offshore. This new subduction zone will result in a chain of new andesitic volcanoes, and thus new continental material developing offshore. The weakness in the continental margin between the new island chain and the original super-continent allows spreading to occur creating a trough called a back-arc basin. The area west of the islands of Japan is an example of this.

Now, marginal seas and island arcs surround the super-continent. Back-arc basins eventually fill with sediment, thus extending the size of the super-continent.

Eventually, due to the presence of weaknesses in the zones that were once marginal seas, the super-continent is able to split up, allowing the formation of separate continents, like we see today.

The cycles continue for each continent. If subduction of the ocean plates continues, it may bring continents together once again creating a supercontinent and thus the cycle can continue.

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-Analyse information from a geological or tectonic map of Australia in terms of age and/or structure of rocks and the pattern of growth of the continent

The picture below shows that the different parts of Australia are of different ages. The oldest parts are the Pilbara and Yilgarn Cratons in Western Australia, which were cratonised before 2500Ma ago. Note that most of Eastern Australian is less than 500 Ma old. In general terms Australia has grown from west to east as we view it now and it continues to grow to our north in Papua New Guinea.

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Name: ArchaeanEon: Archaean Time: Before 2500MAFacts:

Tectonic processes at this time, were very different to those today There was much more heat in the mantle Convection was more rapid and chaotic There was a thinner lithosphere and more molten material in the mesosphere Two types of material formed:

1. Belts of heavily metamorphosed granulite-gneisses2. Greenstone belts

During the late Archaen the small cratons came together to form a single but not very rigid supercontinent

Diverse microbial life flourished in the primordial oceans Continental shields developed from volcanic activity Reducing (anaerobic) atmosphere enabled anaerobic microbes to develop Plate tectonics followed a different regime of continental drift One type of organism the Cyanobacteria (blue-green algae) produced oxygen as a

metabolic by-productName: Proterozoic Eon: Proterozoic Time: Between 2500MA and 545 MAFacts:

Atmosphere changes from reducing to oxygenated Original anaerobic inhabitants of the Earth restricted into a few anoxic refuges Rise of aerobic life Stromatolites were common During the period 2500 to 900 MA the development of the continent was complex

and its interpretation remains open to debate Then Australia consisted of Archaean and early Proterozoic cratonic nuclei (Yilgarn,

Pilbara and Gawler cratons) separated by linear fold belts such as the Central Australian mobile belt

Mobile belts were progressively cratonised, finally welded and consolidated into the Australian Precambrian Craton 900 MA ago

Supercontinent Rodinia formed (1120-850 MA) The supercontinent Sturtia formed (720-560 MA)

Name: PhanerozoicEon: PhanerozoicTime: 545MA to presentFacts:

Devonian, Mesozoic Palaeozoic:

-The further development of eastern Australia is marked by the eastward movement of subduction zones-A volcanic island arc ran through what is now Western Victoria and was accreted to the continental coast

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-During the Ordovician there was a subduction zone in what is now central NSW and this was accreted to the continental coast

Oogenesis:-The process of mountain building-Can take tens of millions of years and build mountains from plains or even the ocean floor-Can occur due to continental collision or volcanic activity-Frequently rock formations that undergo orogeny are severely deformed and undergo metamorphism-Usually produces long linear structures, known as Orogenic belts associated with subduction zones

Palaeozoic continued-During the Silurian and Devonian the subduction zone moved east again to the New England extending northwards in Queensland

During the late Carboniferous to the Triassic the supercontinent Pangaea was forming By the end of the Triassic all of Eastern Early Cretaceous, sea floor spreading began in north western Australia and moved

down the western edge of the continent as India moved away from Aus and the Indian ocean grew

Rifting occurred on the southern margin of the continent resulting in the formation of the Tasman sea

Papua New Guinea began to form in the Early Cretaceous as the pacific plate was subducted under the Australia-Indian plate

In the last 5 MA New guinea has risen some 6 KM-Present information as a sequence of diagrams to describe the plate tectonic super-cycle concept

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Focus Area 4- Natural disasters

-Identify where earthquakes and volcanoes are currently likely to occur based on the plate tectonic model-Most volcanoes and earthquakes will occur on plate boundaries.-Shallow focused earthquakes, down to depths of seven kilometres, will occur along those sections of transform faults that are between the spreading rift axes.-Earthquakes and explosive volcanoes will be produced in subduction zones. Shallow focused earthquakes will occur near the ocean trench; deep focused earthquakes will occur further away from the trench.-Earthquakes will frequently occur at conservative boundaries, down to depths of 30 kilometres.-Volcanic eruptions occur progressively along the rifts of the mid ocean ridges. More activity will occur away from the hinge of rotation for the two plates.-Relatively passive eruptions can be expected from volcanoes located at divergent boundaries.-Mid plate volcanoes are usually the result of a hot spot under the plate. Observation of the direction of plate movement over the hot spot can assist in predicting where new volcanos will occur.

The plate tectonic model does not currently provide reliable predictions related to earthquakes in continental lithosphere.

-Describe methods used for the prediction of volcanic eruptions and earthquakes

Technology How it is used

Radar images Images taken from satellites before earthquakes, show horizontal and vertical shifts in the ground surface. This can be used to predict what could happen in the future. Radar images from satellites show the topography of the land and can help to detect the history of past earthquakes. When radar images are combined with other information including seismometers and GPS, it is easier to detect when an Earthquake may occur

Magnetometers: Magnetometers measure the magnitude and direction of a magnetic field. The magnetic field of the Earth changes as strain in rocks vary, so changes in magnetism may warn that plates are moving. Magnetism is measured by using magnetometers. They can distinguish between general changes and changes caused by tectonic plate movements

GPS Stations: Global Positioning Systems receive satellite signals which are transmitted to an observatory. Signals record the exact location of the GPS. Changes in positions indicate the crust has moved. Scientists can monitor changes in direction, speed and altitude of plates.

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Creep meters Used to measure ground movement, or creep. A wire is stretched between two rods on either side of the fault. A weight is placed at one end of the wire which lines up with a scale. Measurement changes if the fault moves. Blocks of crust along faults either move in a slow and steady motion known as a creep, or they jolt in a violent and sudden movement. Creeping movements cause small to moderate earthquakes. Sometimes the creeping areas along a fault become stuck. Seismic activity drops and a seismic gap results

Seismometers Seismometers are used to record vibrations in the ground. They are incredibly sensitive and can pick up even the slightest tremors. Many are powered by solar energy. All of the earth’s seismic activity can be recorded from vibrations in the Earth’s crust and drawn onto a seismogram. Signs of tiny earthquakes recorded may mean that a volcanic eruption can occur

-Describe the general physical, chemical and biotic characteristics of a volcanic region and explain why people would inhabit such regions of risk

-Volcanic regions have extremely fertile soils. Volcanic rocks break down physically and chemically very quickly. Volcanic rocks weather readily producing soils rich in iron and magnesium . Soil formation can occur in as little as a few hundred years, but there are instances recorded of seeds germinating on erupted rock soon after cooling. Volcanic mountains often have very high altitudes resulting in favourable conditions for plentiful rainfall-There is generally a great diversity of biota in volcanic regions. If adequate rainfall is available, natural vegetation and crops grow quickly and these can support a great variety of animal species-Volcanic landscapes have aesthetic attraction for people. Mountains create beautiful scenery and symmetrical volcanic cones have been important to many cultural beliefs-People are often willing to take the risk that eruptions will not occur in their lifetime. Many people who live in volcano and earthquake prone regions accept earthquake activity, like climate, as a condition of life.

-Describe hazards associated with earthquakes, including ground motion, tsunamis and collapse of structures

Ground motion can cause built structures to collapse, can damage and displace vehicles, can cause water in harbours to be displaced, and can trigger other devastating events such as landslides and mudslides. People and other animals can be buried in crevasses.

Major earthquakes in the lithosphere below oceans can trigger tsunamis. Such earthquakes can change the level of the ocean floor by several metres and displace an enormous volume of water. The waves produced contain the energy of the earthquake as it lifts up to 14 kilometre of ocean above it. A wave generated has twice the wavelength of the diameter of the affected area and it travels very fast (800 km per hour). Upon reaching shallow water, the front of a tsunamis wave-set slows down while the back catches up to produce a

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massive wall of water. Tsunamis devastate low lying coastal areas. Houses and other structures are usually hit by a wall of water from the ocean and again as the water rushes back out to sea. Floating debris increases the impact on life and property.

-Describe hazards associated with volcanoes, including poisonous gas emissions, ash flows, lahars and lava flows and examine the impact of these hazards on the environment, on people and other living things

One of the greatest hazards of volcanoes is the explosive eruption. At least 200 000 people have lost their lives as a result of explosive volcanic eruptions in the past 500 years. Well known examples of explosive eruptions are:-Mt Pelée, Martinique, in which erupted in 1902, killing 30 000 people-Mt St Helens, USA, which erupted in 1980 resulting in 57 dead or missing and $1.2 billion damage.

Poisonous gas emissions from volcanoes include carbon monoxide (CO), sulfur dioxide (SO2), sulfur trioxide (SO3), hydrogen sulfide (H2S) hydrochloric acid (HCl), hydrofluoric acid (HF), sulfurous acid (H2SO3) and boric acid (H3BO3). Carbon dioxide (CO2), although not poisonous, can asphyxiate by displacing air that contains oxygen. Most of these emissions are associated with eruptions. One specific example recently occurred in Lake Nyos, in Africa, where the crater-lake became saturated with carbon monoxide gas. A minor disturbance in the lake caused about one cubic kilometre of gas to be released, killing 1700 people in a nearby village and all livestock in surrounding areas.

Ash flows can kill because of heat and poisonous gas. In March and April 1982, El Chichon in Mexico erupted three times producing high velocity incandescent ash flows that levelled villages up to eight kilometres away. The number of deaths exceeded 500. In 79 AD, Mt Vesuvius buried the cities of Pompeii and Herculaneum so completely that they weren’t discovered again until 1700 years later.

Different types of lava flow at different speeds. Highly viscous lava tends to block volcanic vents and lead to explosive eruptions. High temperature, low viscosity lava flows freely and is often associated with hot spot volcanoes and sea floor rifts. These lavas do not usually endanger human life because there is time for evacuation. However all property in their path is destroyed by the lava. Lava flows regularly from Mt Etna in Italy and Kilauea in Hawaii. Villages are buried but people have enough time to escape the flow.

Lahars are mud and ash flows generated from the melting of an ice cap on a volcano or associated with release of water from a crater lake. Flows of volcanic debris can have the consistency of wet cement. They can sweep down the sides of a composite volcano burying everything in their path. Nevada del Ruiz Volcano, in Colombia, buried the city of Armero with a lahar, killing 25 000 people.

A nuée ardente is a highly mobile, turbulent gaseous cloud erupted from a volcano. It can be incandescent. The most infamous nuée ardente occurred when Mt Pelée erupted in 1902, killing 30 000 people.

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-Justify continued research into reliable prediction of volcanic activity and earthquakes Some possible arguments for continued research are:-There are large populations in many areas prone to volcanic activity and earthquakes. Given that prediction of impending volcanic eruptions and earthquakes are currently unreliable, people will not move until it is too late. Thus reliable early warning would save many lives and reduce losses due to poor preparation for a disaster.-Although research and the use of new technologies are expensive, the cost is small compared to the possible savings in lives, the provision of emergency services and loss of work, after a devastating event.-The use of new technologies, such as modern microcomputers, and remote sensing technologies, offer great potential for reliable methods of prediction to be developed in the near future.

Some alternative arguments:-Earthquakes are difficult or impossible to predict because of their inherent random behaviour. Efforts should be channelled into hazard mitigation.-Providing warnings can cause panic in a population, potentially causing more problems than if an earthquake or a volcanic eruption was not predicted.-The geological hazards of most regions are now known and the choice to live in a potentially hazardous area is an individual one. Education about ways to survive and cope with the effects of a natural disaster is more appropriate than continued research into prediction.

-Describe and explain the impacts of shock waves (earthquakes) on natural and built environments

Shockwaves from earthquakes are of three main types:

1. P-waves are compression waves.2. S-waves are transverse or shear waves.3. L-waves are surface waves and can be transverse or elliptical. The elliptical waves are

the slowest, but often the largest and most destructive, of the wave types caused by an earthquake.

The impact of shockwaves is related to their intensity.Factors affecting intensity include the location of the focus, the triggering mechanism, the quantity of energy released and the nature of the local geology.

Earthquake intensity is measured using a relative scale, such as the modified Mercalli scale.

The magnitude of an earthquake is an absolute value and is related to the amount of strain energy released, as recorded by seismographs. Magnitude is measured on the Richter scale, a numerical scale that describes an earthquake independently of its effects on people or objects such as landforms or buildings.

The following table relates some of the Modified Mercalli scale of earthquake intensities to some well-known examples. The Richter scale values are provided for comparison.

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Intensity (Mercalli)

Title Effects on natural and built environments

Example(Richter magnitude)

II Feeble Suspended objects swayIV Moderate Windows and dishes rattle Port Jackson, 1788

Rather strong

Dishes and windows broken Lithgow, 1985 (4)

VI Strong Chimneys toppleVIII Destructive Weak structures severely

damaged; strong structures slightly damaged

IX Ruinous Total destruction of weak structures. Foundations damaged. Underground pipes broken

Meckering, 1968 (5) Newcastle, 1989 (5.6)

X Disastrous Only best buildings survive. Ground badly cracked

XI Very disastrous

Few masonry structures remain standing. Broad cracks in ground

Kobe, 1995 (7.2)Western India, 2001 (7.9)

XII Catastrophic

Total destruction. Waves seen on the ground

Chile, 1960 (9.5)

-Distinguish between plate margin and intra-plate earthquakes with reference to the origins of specific earthquakes recorded on the Australian continent The Australian continent lies entirely within the Australia-India plate, and so it does not experience plate boundary processes.-Plate margin earthquakes account for ninety percent of all earthquakes and are the result of the constant movement of the rocks at plate boundaries against each other.-Intra-plate earthquakes are those that occasionally occur in the crust of plates and away from the more active plate boundaries. The causes of intra plate earthquakes are not well understood, but they are usually caused by compressive stress in rocks.-Australia has three distinct regions of earthquake activity. These are:

the Eastern region, covering the eastern highlands and coastal areas the Central region, extending from near Adelaide to the Simpson Desert the Western region, encompassing several distinct zones.

-The most disastrous Australian earthquake in the last 200 years was the Newcastle earthquake of 28 December 1989. It was a magnitude 5.6 earthquake that caused $1.2 billion damage. The most likely cause was by readjustments along the Hunter-Mooki Thrust, a curved fault running from Newcastle and through Maitland, Murrurundi, Quirindi. Narrabri and Mackay, The fault is sporadically active due to strong easterly compression from the expanding Pacific Ocean floor.-In the central seismic region of Australia, earthquakes have been associated with a 120 kilometre long fault as a result of north-south compressive forces-The stress causing intra-plate earthquakes may be associated with isostasy, which is the tendency for rock masses to rise or sink to achieve a balance between downward weight forces and upward buoyancy forces. Erosion and deposition change historically balanced isostatic forces, causing new regions of stress and strain.

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-Some intra-plate earthquakes may be related to the stress at plate boundaries and to temperature changes in the lithosphere caused by processes in the mantle. The Australian plate has many north-south trending concentrations of earthquakes, so it may be that the Australian plate is adjusting to the twisting motion of the plate as it moves north. The forces that drive the continent may not be uniform and adjustment to the different stresses created by this may cause the earthquakes.-In Western Australia, a linear zone of seismic activity extends from near Moora, southeast to Albany. This is known as the Southwest Seismic Zone. It is the most seismically active area in Australia. The town of Meckering, that experienced a magnitude 6.9 earthquake on 14 October 1968, lies within this zone. Though the reason for the concentration of seismic activity in the Southwest Seismic Zone remains unknown, it could be caused by a major structure/discontinuity of crustal or lithospheric scale that has been reactivated.

-Gather, process and present information from secondary sources to chart the location of natural disasters worldwide associated with tectonic activity and use available evidence to assess the patterns in terms of plate tectonics

ONE NOTE

-Gather information from secondary sources to identify the technology used to measure crustal movements at collision boundaries and describe how this is used ONE NOTE

Gather information from secondary sources to present a case study (2011 Christchurch Earthquake) of a natural disaster associated with tectonic activity that includes: – An analysis of the tectonic movement or process involved February 22nd 2011-Earthquake in Christchurch magnitude 6.3 hit 20km South East of Christchurch 5km in depth. Aftershock of Canterbury earthquake 5 months ago situated 20 miles (32km) west of the city with a magnitude of 7.1. New Zealand situated on the Pacific and Australian plate boundary causing major seismic activity. Cause of this earthquake: a previously unrecognized fault at a conservative boundary, an offshoot from the Alpine fault– Its distance from the area of disaster Most earthquakes near Christchurch occur due to the Alpine fault, a conservative plate boundary 100km from Christchurch. This earthquake was caused due to a new fault, or a fault which has previously gone unrecognized– Predictions on the likely recurrence of the tectonic movement or process The high magnitude of this earthquake lessens the chance of another major earthquake in this region for a large period of time – Technology available to assist prediction of future events Radar images: Images taken from satellites before earthquakes, show horizontal and vertical shifts in the ground surface. This can be used to predict what could happen in the future. Radar images from satellites show the topography of the land and can help to detect the history of past earthquakes. When radar images are combined with other information including seismometers and GPS, it is easier to detect when an Earthquake may occurMagnetometers: Magnetometers measure the magnitude and direction of a magnetic field.

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The magnetic field of the Earth changes as strain in rocks vary, so changes in magnetism may warn that plates are moving. Magnetism is measured by using magnetometers. They can distinguish between general changes and changes caused by tectonic plate movementsGPS Stations: Global Positioning Systems receive satellite signals which are transmitted to an observatory. Signals record the exact location of the GPS. Changes in positions indicate the crust has moved. Scientists can monitor changes in direction, speed and altitude of plates. Seismometers: Seismometers are used to record vibrations in the ground. They are incredibly sensitive and can pick up even the slightest tremors. Many are powered by solar energy. All of the earth’s seismic activity can be recorded from vibrations in the Earth’s crust and drawn onto a seismogram. Signs of tiny earthquakes recorded may mean that a volcanic eruption can occurCreepmeters: Used to measure ground movement, or creep. A wire is stretched between two rods on either side of the fault. A weight is placed at one end of the wire which lines up with a scale. Measurement changes if the fault moves. Blocks of crust along faults either move in a slow and steady motion known as a creep, or they jolt in a violent and sudden movement. Creeping movements cause small to moderate earthquakes. Sometimes the creeping areas along a fault become stuck. Seismic activity drops and a seismic gap results– An investigation of possible solutions to minimise the disastrous effects of future events Earthquakes cannot be predicted, however, the effects of earthquakes can be minimised. Buildings in earthquake prone areas are built stronger so they can survive earthquakes. Earthquake-proof buildings are built on concrete rafts and reinforced. This is so that when the ground shakes, the whole building sways and stays in one piece

Focus Area 5- Plate tectonics and climate

-Predict the possible effects of explosive volcanic activity on global and local climates Global effects:-Explosive volcanism will produce large amounts of ash and aerosols that can reach into the stratosphere. The high levels of material in the atmosphere at this height will rest in a reduced amount of radiation from the sun reaching the Earth’s surface. Less radiation reaching the surface reduces the surface temperature and the heating of air in contact with the surface. If widespread enough, there will be a reduction in the global temperature.Local effects:-Fine ash will increase precipitation in the area around a volcano.-The precipitation will be acidic because of the reaction of sulfur dioxide with water in clouds developing around the volcano.-There may be reduced local temperatures because of reduced radiation if a volcanic plume persists for a prolonged time.

-Describe and explain the potential and observed impacts of volcanic eruptions on global temperature and agricultureThe potential impacts of volcanic eruptions on global temperature:The injection of sulfur dioxide (SO2 ) into the stratosphere causes the greatest impact on the atmosphere and global temperatures. The SO2 converts to sulfuric acid aerosols that block

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incoming solar radiation and contribute to ozone destruction. The reduction in solar radiation can cause global cooling. The plume of ash from an eruption causes an increase in the amount of sunlight reflected by the Earth's atmosphere back to space causing the surface of the planet to cool.The potential impacts of volcanic eruption on agriculture:Volcanic eruptions have the potential to devastate agricultural activity. Areas close to the erupting cone can be destroyed by lava and mud flows. Poisonous gases can kill herds of stock. Areas further from the cone can be covered in thick layers of pyroclastic debris.The observed impacts of volcanic eruption on global temperature:El Chichon and Mount Pinatubo emitted the greatest amounts of SO2 into the stratosphere. El Chichon produced about 7 million tonnes of SO2 and Mount Pinatubo produced about 20 million tonnes. Both of these volcanoes are at low latitudes but they both had high eruption rates. The impact of eruptions may not last very long. For a large eruption like Mount Pinatubo, the impact may last for up to three years.The observed impacts of volcanic eruption on agricture:Mt St Helens produced a layer of debris six-tenths of an inch (about 15mm) thick, five hundred miles (about 800km) away. In the regions affected by Mt St Helens:-Crop loss was estimated at $100 million, or seven percent of the national crop value for that region.-Fifty percent of the alfalfa hay crop was ruined-Timber to the value of $100 million dollars was destroyed

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